Is there a musical theory of harmony or a system of chord-understanding that does not rely on the 12-tone temperament?
For example, a fretless instrument has (theoretically) an infinity of tones between one note and the next. Thus, the concept of note becomes blurry and the point of interest becomes the interval (or frequency-distance) between tones.
Therefore, I am curious if there is a (more-or-less magical) conjoined theory that works on a continuous (or non-quantized temperament).
If not, is there any research or have there been past attempts at a system ?